The use of syringes for the hypodermic withdrawal of blood from a patient's body through a hollow needle detachedly forming a part of a syringe is commonplace in modern medicine. One reason to take blood from a patient is to obtain an arterial blood gas sample. Air is almost always included within the syringe barrel or needle after filling the syringe barrel with blood. For example, aspiration of a sample through a needle or the incomplete filling of a syringe may draw air into the syringe. There are many instances in which such air can contaminate an arterial blood gas sample. In taking an arterial blood gas sample, the purpose is to evaluate the patient's blood gas levels (i.e., carbon dioxide and oxygen) or to evaluate other variables which depend upon blood gas levels (i.e., pH levels), therefore the introduction of air into the sample would serve to alter the true concentrations in the blood and cause subsequent analysis of data to be misleading. It is therefore desirable to remove any air from the blood sample as quickly as possible after removal of the blood from the patient's body.
Accordingly, one technique for removing air from a freshly-filled syringe is to tilt the syringe upward so that the air bubbles rise to the top of the syringe barrel and the plunger is advanced into the barrel to purge the air through the needle tip. Although this technique works well in removing air from the syringe body and needle, it may also cause some blood to be expelled from the tip of the needle. The blood may be expelled either if the plunger is pushed too aggressively or if blood is trapped by capillarity in the uppermost portion of the luer, needle hub or needle.
Typically, the purged air and liquid spray from the needle would be simply squirted into the air or into a pad of gauze material. However, with the great concerns today about the transmission of various diseases such as AIDS and hepatitis, great care must be taken in the removal of such blood spray from an arterial blood gas sample and further in the handling and disposal of hypodermic syringe needles used with such syringe systems.
Many prior art patents dealing with the blood sample air-contamination problem concentrated on expelling contaminating air from the syringe while the syringe was being filled with the patient's blood. U.S. Pat. Nos. 3,978,846 and 4,340,067 disclose devices incorporating self-sealing hydrophilic filters into the body of the syringe. When dry, a self-sealing type hydrophilic filter allows air to pass through it and out of the syringe. The syringe-filter system fills with blood because a pressure differential between the luer opening and the filter is created by the patient's arterial pressure. This air pressure differential helps force air through the filter and out of the syringe. When all of the air is expelled, the leading edge of the blood contacts the filter. When wetted by the blood, the self-sealing nature of the filter causes it to expand and prohibit passage of both air and liquid. However, the utility of these type of self-sealing hydrophilic systems does not extend to post filling contaminations because the already wetted filter will no longer pass air and so it can not be utilized to purge any remaining air or air introduced at later times. Also, such filters have not always self-sealed in the proper manner thereby allowing blood to seep out of the plunger end of the syringe body possibly causing dangerous contamination of medical personnel.
U.S. Pat. Nos. 4,769,026 and 4,775,376 to Strung disclose syringe purging devices that address the problems of post filling contamination. These devices utilize separate containers which are either airtight or are equipped with hydrophobic filters. Hydrophobic filters allow for the passage of air but not liquid. Various embodiments of these patents also include a deactivating substance for neutralizing the hazardous fluids which are to be injected into the container. In use, the container and syringe are attached in an airtight fit, air and blood from the syringe are injected into the separate container by advancing the syringe plunger until the air has been evacuated from the syringe. However, such a device is overly complicated for the uses intended for the present invention. An airtight chamber is neither necessary nor desirable for the present invention. Furthermore, a deactivating substance involves an unnecessary complication and expense.
U.S. Pat. No. 5,125,415 to Bell discloses a syringe tip cap utilizing a self-sealing hydrophilic filter in a separate chamber for allowing for the purging of air from the syringe body. However, the syringe tip cap disclosed in Bell can be used only after the needle and hub assembly has been removed from the syringe body. Typically, the sequence of events by a nurse technician or other medical personnel in taking an arterial blood gas sample would be as follows. First, the technician would remove the blood filled needle and syringe barrel assembly from the patient's arm or any other injection site with one hand while depressing the injection site with the fingers of their other or second hand. The needle and syringe barrel assembly is set aside while the patient's arm is properly bandaged. Next, the technician would remove the needle and needle hub from the syringe barrel and properly dispose of them into a protective sharps container. Then, the syringe tip cap would be attached to the distal end of the syringe barrel, the syringe barrel would be held in an upside down position or held with the distal end pointing upwardly while the technician advances the plunger to purge any air bubbles with attendant liquid blood spray out of the syringe barrel and into the absorbent filter of the syringe tip cap.
The above sequence of events is undesirable in that the air bubbles were allowed to remain in the blood sample for a significant period of time while the technician was bandaging the patient's arms and removing and disposing of the needle and hub assembly into a protective sharps container. It is possible that the blood sample would be significantly contaminated by the air existing within the blood sample so as to provide erroneous blood gas levels such that subsequent analysis of this data to be misleading.